KV6 engine racing

[SD1too]

Hi Stefan, it's good to hear from you. Here are the answers to your questions.

The throttle body is the original. Earlier in this thread I described how I have bought a new one only to find the fault still exists.

The throttle cable is the original. Yes, it is routed correctly; you know how meticulous I am about things like that!

The tickover does not return to normal with a quick slap down on the pedal. However, if the engine is stopped and immediately restarted, the idle will be normal. This is the most baffling thing of all and it appears to rule out the cable faults you have described.
When driving, the engine response to throttle inputs is faultless. It's only when the pedal is released that the car's deceleration is abnormally slow but I can see that the throttle linkage is definitely at the closed position. It's not being held open. Consequently I have not cleaned or lubricated the inner throttle cable and I haven't detected any drag on the cruise control actuator either.

You might have read that I'm rebuilding the top end of a friend's KV6 after the aftermarket water pump seized and caused the cambelt to shred. It's almost complete except for refitting the manifold chamber/throttle body and the owner is allowing me to fit that to my engine for testing purposes. I'm collecting it on Friday.

Thanks for your interest Stefan, much appreciated.

Simon

[xsport]

Hope you get a positive response with a new manifold trial. That said , you would still need to find a cause . Is there any play at all between butterfly and control cable turning of the lever , up and down or oval wear of the spindle mechanism ? All quite relative checks to find any play or back movement. Should the exchange manifold/ throttle body not be prove to be fruitfull, do you think engine timing may be advancing upon throttle opening ? Im not quite sure how this is achieved , but would think the engine control unit would be in control of this via the anti knock sensors input and other sensors for timing inputs. Maybe a clean up of the ECU pins and further investigation on t4 could help. I hope that the transplant is indeed successful,and then at least you will be in a position to eliminate causes. It is indeed a strange one , that is of course that the obvious culprits have been eliminated. I would imagine it is quite frustrating for what seems ,on the surface , to have an easy solution. I know you are in two places at once at the moment ,but give us an update when your any further down the line in sorting. All the best ...

[xsport]

Just as an aside simon, when i changed my throttle body complete , i was advised that it would need T4 to be introduced to the system. This was when i collected it from the MGROVER franchised supplier. This was not the case ,it worked perfectly. What i have read elsewhere is that the positioning inside the body of the throttle housing, for the throttle position sensor ,has a critical starting position,and if removed ,needs to be marked before hand and refitted in the same position. May be of little significance, or not ,but could be worth mentioning. ...

[SD1too]

Thank you for your further thoughts Stefan.

Originally Posted by xsport

Is there any play at all between butterfly and control cable turning of the lever , up and down or oval wear of the spindle mechanism?

All that was invalidated when a brand new throttle body was fitted with zero improvement.

Originally Posted by xsport

... do you think engine timing may be advancing upon throttle opening ? Im not quite sure how this is achieved, but would think the engine control unit would be in control of this ...

Yes, ignition timing is controlled by the ECM. I've been working on the basic principle that for the engine to run faster there needs to be an additional supply of air. Tests suggest that this is entering downstream of the throttle butterfly since the idle stepper motor is unable to control it. I'd expect an ignition timing fault to cause rough running, even stalling, a fault code to be logged and probably the "check engine" light to illuminate but there is none of this. The engine runs smoothly. But the honest answer is that I don't know Stefan. How would I prove that?

Originally Posted by xsport

Maybe a clean up of the ECU pins and further investigation on t4 could help.

cb750Chris spent a whole day with his T4 but it didn't show any live data errors other than the idle speed was higher than the ECM's target. Well, we know that!

Originally Posted by xsport

I would imagine it is quite frustrating for what seems ,on the surface , to have an easy solution.

Originally Posted by xsport

What i have read elsewhere is that the positioning ... for the throttle position sensor ,has a critical starting position ...

That appears to be a myth Stefan. RAVE's instructions are simply to take care that the flat on the throttle spindle mates properly with the sensor, to apply pressure only in the centre and to rotate it only anticlockwise to align the fixing holes. All of this is straightforward.

There is then a contradiction. The repair manual says that a throttle initialisation procedure must be followed using T4 if the sensor is removed or renewed, yet the technical description states that (for the KV6) the closed throttle position is automatically learnt by the ECM during driving. T4 does however have several idle control "adaptations" which were all reset by cb750Chris but had no effect.

Simon

[StewartIngram]

Where are you based, anywhere near Cambs? I have spare manifolds/throttle bodies from which you could borrow one. (All were working when removed, but have had some parts removed at various times, though I'm sure I have all those parts stored as well).

[xsport]

I of course do not know a great deal at all about T4 and its operation.In fact zero !! What i do recall is that when philt4 gave my car some attention he did reset all settings back to factory. Im sure that probably what has been done on the T4 for you would have been carried out. I can remember years ago that whilst manually setting my "points" on a mk3 cortina ,whilst running on idle .that a significant increase in tick over speed could be achieved . It could be set to around 1200 rpm without any issues !! This was without any use of the throttle cable increase,just purely on idle. I know that this is a different beast all together and set up ,but it shows it is possible . And by the way ,it went like a rocket,no pinking and pulled like hell !! Lets just hope your manifold transplant works for you simon. Many thanks to stewart for his kind offer ,which i hope will not be needed , so fingers crossed. ..

[SD1too]

Originally Posted by StewartIngram

I have spare manifolds/throttle bodies from which you could borrow one.

Thanks very much for the offer Stewart but I'm o.k. for now as I'm picking up a loan manifold chamber tomorrow.

Simon

[SD1too]

I have now fitted the loan throttle body/manifold chamber assembly from my friend's car (undergoing repairs) to my engine. My idle is now perfect, stable and lower than it's ever been.

Although I've yet to identify the exact fault, I now know that it's nothing to do with my ECUs, vacuum tubing or wiring. I had already eliminated by substitution the idle stepper motor, throttle position sensor, air temperature & pressure sensor and the VIS power actuator seal. I had also disabled the purge valve all to no effect. So apart from the VIS balance actuator seal, all that remains is the manifold chamber moulding which appears to have been manufactured in two parts, welded and screwed together.

Incidentally upon starting the engine after the exchange, the idle was absolutely perfect straight away. No setting-up was performed with any diagnostic equipment nor did I press the accelerator multiple times as is described for the K series MEMS ECM.

Does anyone have any ideas how I can find the air leak?

Simon

[xsport]

Well thats good news simon ! Now at least you have your way forward. I know you will have inspected the plastic chamber visually and probably found nothing un towards. Are the rubber seals in good condition without compression set ? I would be looking at the black rear firewall bank internal seals in particular and checking for folding over . It helps with a good knob of red rubber grease or similar when mounting and of course sealing. There may be splits/cracks around the rear black seals ares for you to check , as these are more difficult to seat when the manifold is re-assembled after removal. Can i ask if you have any open screws missing at the rear mounting rubber area ( the ones that snap off ,and are a pain to relocate ) . Other than these points, suspect a crack/broken seal along its joint surfaces where the manifold was joined in manufacture. Apologies if all these have been closely inspected ,knowing how thorough you are, but nothing lost to check again . Also check the purge valve seal , i know you disabled this but have you checked the seal on this to the manifold.? Plenty to keep you going simon ... especially with more than one job on the go ..

[Matt_75]

Originally Posted by SD1too

Does anyone have any ideas how I can find the air leak?

You could try a smoke machine fed into the inlet, like this one:

https://www.ebay.co.uk/itm/256013071...mis&media=COPY

I've never used one myself but have seen YouTube videos of them being used to check for air leaks.